Final Anderson Dam seismic study concludes that storage restrictions can be modified but dam must be retrofitted

SAN JOSE, CA – The Santa Clara Valley Water District has completed a seismic stability study on Anderson Dam. The study confirmed preliminary findings that the dam is subject to significant damage if a large earthquake were to occur within two kilometers of the dam.

A rigorous analysis indicated that a storage restriction that has been in place since October 2010 could be safely adjusted, allowing 12 additional feet of storage. The two responsible regulatory agencies, the California Division of Safety of Dams and the Federal Energy Regulatory Commission, approved the adjustment allowing the dam to fill to 68 percent of its capacity, up from 57 percent.

The water district has initiated a capital project to complete the planning, design and construction of a seismic retrofit by the end of 2018. The operating restriction will remain in place until the project is completed.

The retrofit project has yet to be designed. During construction, expected to begin in 2015, it is likely that reservoir levels will have to be reduced. The determination about the levels of reduction will be based upon the construction project plans. Currently, the reservoir is 64 percent full which is just under the historic norm for this time of year.

Background:Built in 1950, Anderson Reservoir is the largest reservoir in Santa Clara County, with a capacity of 90,373 acre-feet of water (29 billion gallons). The reservoir is located on Cochrane Road east of Morgan Hill.

The water district plans to complete seismic safety evaluations on eight of its dams by 2013. The reservoirs are an important component of Santa Clara County’s water supply, but also provide environmental benefits and recreation. In addition, the reservoirs help provide flood protection for homes and businesses downstream.